1. Field of the Invention
The present invention generally relates to computer-implemented methods, carrier media, and systems for generating a metrology sampling plan. Certain embodiments relate to a computer-implemented method that includes generating a metrology sampling plan such that one or more areas on a wafer in which one or more individual defects, included in a population of defects located in a predetermined pattern on the wafer and having one or more abnormal attributes, are located are sampled during metrology.
2. Description of the Related Art
The following description and examples are not admitted to be prior art by virtue of their inclusion in this section.
Fabricating semiconductor devices such as logic and memory devices typically includes processing a substrate such as a semiconductor wafer using a large number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. For example, lithography is a semiconductor fabrication process that involves transferring a pattern from a reticle to a resist arranged on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing (CMP), etch, deposition, and ion implantation. Multiple semiconductor devices may be fabricated in an arrangement on a single semiconductor wafer and then separated into individual semiconductor devices.
Inspection processes are used at various steps during a semiconductor manufacturing process to detect defects on wafers to promote higher yield in the manufacturing process and thus higher profits. Inspection has always been an important part of fabricating semiconductor devices. However, as the dimensions of semiconductor devices decrease, inspection becomes even more important to the successful manufacture of acceptable semiconductor devices because smaller defects can cause the devices to fail. For instance, as the dimensions of semiconductor devices decrease, detection of defects of decreasing size has become necessary since even relatively small defects may cause unwanted aberrations in the semiconductor devices.
Another important part of manufacturing yield control is determining the cause of defects on the wafer such that the cause of the defects can be corrected to thereby reduce the number of defects on other wafers. Often, determining the cause of defects involves identifying the defect type and other attributes of the defects such as size, shape, composition, etc. Since inspection typically only involves detecting defects on the wafer and providing limited information about the defects such as location on the wafer, number of defects on the wafer, and sometimes defect size, metrology is often used to determine more information about individual defects than that which can be determined from inspection results. For instance, a metrology tool may be used to revisit defects detected on a wafer and to examine the defects further in some manner either automatically or manually.
Metrology processes are also used at various steps during a semiconductor manufacturing process to monitor and control the process. Metrology processes are different than inspection processes in that, unlike inspection processes in which defects are detected on a wafer, metrology processes are used to measure one or more characteristics of the wafer that cannot be determined from currently used inspection tools. For example, metrology processes are used to measure one or more characteristics of a wafer such as a dimension (e.g., line width, thickness, etc.) of features formed on the wafer during a process such that the performance of the process can be determined from the one or more characteristics. In addition, if the one or more characteristics of the wafer are unacceptable (e.g., out of a predetermined range for the characteristic(s)), the measurements of the one or more characteristics of the wafer may be used to alter one or more parameters of the process such that additional wafers manufactured by the process have acceptable characteristic(s).
There are, however, a number of disadvantages to using metrology processes and tools to measure one or more characteristics of a wafer for process monitoring and control applications. For example, most metrology tools are relatively slow, particularly compared to inspection systems. Therefore, metrology processes are often performed at one location or a limited number of locations on the wafer such that metrology results may be acquired in a relatively expedient manner. However, many processes used to manufacture semiconductor devices produce wafers that have characteristic(s) that vary across the surface of the wafers. As such, using metrology measurements performed at one location or a limited number of locations on a wafer may not provide sufficient information about the characteristic(s) of the wafers such that the process can be accurately monitored and controlled. Therefore, the sampling plan of the metrology process can significantly affect the meaningfulness and usefulness of the metrology results.
There are, however, a number of disadvantages to currently used metrology sampling plans. For instance, traditional metrology sampling approaches are based on fixed locations on the wafer, which may represent samples across the wafer or may be based on previously known problem areas on the wafer. Measurements may then be performed on given sites until the fixed sample plan is adjusted (e.g., manually). Therefore, one of the disadvantages of currently used metrology sampling plans is that the fixed sites that are sampled during metrology may not be sensitive to subtle variations in the process. For example, in the event that critical dimension (CD) varies in the areas on the wafer that the fixed sampling does not cover, an important excursion may be missed, which may be particularly critical for process development at technology nodes at 65 nm and beyond.
Accordingly, it may be advantageous to develop computer-implemented methods, carrier media, and systems for generating a metrology sampling plan that is more sensitive to subtle variations in a process performed on a wafer such that important excursions in the process do not go undetected.